CBS, the US broadcast network, on Thursday said it had agreed to pay $1.8bn in cash to acquire CNET Networks, a technology and entertainment website operator.

CNET’s shares jumped 43.5 per cent on news of the deal, which would make CBS one of the 10 most popular US internet groups with a combined 54m unique users per month and approximately 200m users worldwide.

The media company, which already operates sites such as CBSSports.com and CBSNews.com, is seeking to ramp up its digital activities at a time when a slowing economy and new technology are pressing the traditional television and radio businesses that supply the majority of its revenues.

CNET, whose sites include News.com, GameSpot.com and ZDNet, claims a total monthly audience of more than 160m people, making it the 10th largest web network.

The deal could end the prospect of a fight between CNET and an activist group led by Jana Partners, a New York-based hedge fund, which had been seeking to appoint new directors to CNET’s board in an attempt to shake up the company.

CBS’s $11.50 a share offer represented a 45 per cent premium to the closing price for CNET stock on Wednesday. It would provide a big return for Jana and its partners, who hold just under 15 per cent of the company’s shares.

Jana declined to comment.

The CBS purchase is the latest in a string of acquisitions – not all successful – of internet-based groups by older media companies, and had been foreshadowed in comments by Quincy Smith, CBS Interactive president, and Les Moonves, CBS chief executive.

Last month, Mr Smith announced that CBS planned to set up a permanent office in Silicon Valley, marking an unusual effort by a traditional media group to plant its flag in the heart of the technology industry.

He added that CBS had been scouring the Valley, meeting 387 potential targets in the past year.

On Thursday he said: “The core businesses of CNET Networks and CBS Interactive represent near-perfect category symmetry in premium online content.

“Together we will have a terrific opportunity to not only grow our established businesses, but to build new attractive verticals of content as well.”

Mr Moonves said: “There are very few opportunities to acquire a profitable, growing, well-managed internet company like CNET Networks.

“Together, CBS and CNET Networks will have significant additional exposure to the fastest-growing advertising sector, and can accelerate our growth through a number of new content, promotion and advertising initiatives.”

During a conference call with investors he added: “When you can combine the entertainment assets, the news assets, the platforms that are available with technology, the cross advertising opportunities, it just gives us great scale.”